The present invention relates generally to a power amplifier, and specifically to improvements in distortion cancellation.
To provide high quality voice communication and handle more calls, telecommunication operators use digital modulation technology and multi-channel carriers. Examples of such technologies include CDMA, TDMA, w-CDMA, and EDGE-GSM. A linear RF power amplifier is needed to transmit digital/multi-carrier waveforms without adding noise, distortions, and adjacent channel interference. A typical RF power amplifier for a base station generates xe2x88x9230 dBc, (dB below carrier) distortion levels which does not meet the emission distortion requirement. Therefore, several linearization techniques have been used to linearize or improve the traditional class AB power amplifier inter-modulation distortion (IMD) performance.
Such linearization techniques for improving IMD include RF feedback, Cartesian feedback, analog pre-distortion, digital pre-distortion and feed forward. The RF feedback and Cartesian feedback techniques improve IMD by 10 dB but both techniques are only useful for narrowband. The feed forward technique improves IMD but at the expense of power loss and efficiency due to adding an output delay line, output couplers and the correction amplifier to the output of the main amplifier. The feed forward technique also is excessive for a CDMA system that requires only xe2x88x9245 dBc IMD. A pre-distortion technique becomes more attractive for such a CDMA system because it does not add the extra system at the output of the power amplifier. However, the digital pre-distortion technique is expensive because it requires very fast A/D, D/A converters and micro-controllers. The traditional analog pre-distortion improves IMD up to 8-9 dB but the gain is not stable and it is useful for only narrow band applications.
What is needed is a cost efficient power amplifier to transmit digital/multi-carrier waveforms with minimum distortion, preferably using a random phase cancellation technique.
The present invention meets this need by providing a cost efficient power amplifier to transmit digital/multi-carrier waveforms with minimum distortion, preferably using a random phase cancellation technique.
A low distortion power amplifier is provided, N being greater than 1, comprising an input divider having an input for receiving an input signal, a first output for outputting a first signal and a second output for outputting a main signal, a carrier cancellation component having an input connected to the input divider for receiving a first signal and an output for outputting a distortion signal, an input attenuator receiving the main signal output from the input divider and producing an attenuated main signal, an input delay device receiving the attenuated main signal from the input attenuator and outputting a delayed, attenuated main signal, and an N way distortion cancellation component having a first input connected to the carrier cancellation component for receiving the distortion signal and a second input connected to the input delay device for receiving the delayed, attenuated main signal and an output for outputting an amplified output signal having low distortion.
The carrier cancellation component for use in the low distortion power amplifier is described, comprising a pre-distortion divider having a first input connected to the input divider for receiving the first signal and an output for outputting a second signal and a third signal, a first delay device connected to the pre-distortion divider for receiving the second signal and outputting a delayed signal, a distorting device connected to the pre-distortion divider for receiving the third signal and outputting a distorted signal, and a carrier cancel combiner having a first input connected to the first delay device for receiving the delayed signal, a second input connected to the distorting device for receiving the distorted signal, and an output for outputting the distortion signal.
The N way distortion cancellation component for use in the low distortion power amplifier is described, comprising a first N way divider connected to the carrier cancellation component for receiving the distortion signal and dividing it N ways into N distortion signals, a second N way divider connected to the input delay device for receiving the delayed, attenuated main signal and dividing it N ways into N delayed, attenuated main signals, N attenuators each connected to the first N way divider for receiving one of the N distortion signals and outputting one of N attenuated distortion signals, N phase shifters each connected to one of the N attenuators for receiving one of the N attenuated, distortion signals and outputting one of N phase shifted, attenuated distortion signals, N combiners each having a first input connected to one of the N phase shifters for receiving one of the N phase shifted, attenuated distortion signals, a second input connected to the second N way divider for receiving one of the N delayed, attenuated main signals and an output for outputting one of N combination signals, N amplifiers each connected to one of the N combiners for receiving one of the N combination signals and outputting one of N amplified combination signals, and an N way combiner connected to each of the N amplifiers for receiving the N amplified combination signals and outputting the amplified output signal having low distortion.
A power amplifier using a pre-distortion technique for reducing distortion, is also provided, N being greater than 1, the power amplifier comprising an input divider having an input for receiving an input signal, a first output for outputting a main signal and a third output for outputting a first signal, a pre-distortion divider having an input for receiving the first signal, a first input for outputting a second signal and a second output for outputting a third signal, a first delay device having an input for receiving the second signal and an output for outputting a delayed signal, a distorting device having an input for receiving the third signal and an output for outputting a distorted signal, a carrier cancel combiner having a first input for receiving the distorted signal, a second input for receiving the delayed signal and an output for outputting a distortion signal, a first N way divider having an input for receiving the distortion signal and N outputs for outputting N distortion signals, an input attenuator having an input for receiving the main signal and an output for outputting an attenuated main signal, a second delay device having an input for receiving the attenuated main signal and an output for outputting a delayed, attenuated main signal, a second N way divider having an input for receiving the delayed, attenuated main signal and outputting N delayed, attenuated main signals, N attenuators each having an input for receiving one of the N distortion signals and an output for outputting one of N attenuated distortion signals, N phase shifters each having an input for receiving one of the N attenuated distortion signals and an output for outputting one of N phase shifting, attenuated distortion signals, N combiners each having a first input for receiving one of the N phase shifting, attenuated distortion signals, a second input for receiving one of the N delayed, attenuated main signals, and an output for outputting one of N combination signals, N amplifiers each having one input for receiving one of the N combination signals and an output for outputting one of N amplified combination signals, and an N way combiner having N inputs each for receiving one of the N amplified combination signals and an output for outputting an output signal.
A low distortion power amplifier using a pre-distortion technique to reduce distortion in the output is described comprising means for receiving an input signal and dividing it in to a main signal and a first signal; means for receiving the first signal and dividing it into a second signal and third signal; means for processing the second signal to produce a delayed signal; means for distorting the third signal to produce a distorted signal; means for combining the distorted signal and delayed signal to produce a distortion signal; means for attenuating the main signal to produce an attenuated main signal; means for processing the attenuated main signal to produce a delayed, attenuated main signal; means for dividing N ways the distortion signal into N distortion signals; means for dividing N ways the delayed, attenuated main signal into N delayed, attenuated main signals; means for processing each of the N distortion signals into N phase-shifted, attenuated distortion signals; means for combining each of the N phase shifted, attenuated distortion signals and the N delayed, attenuated main signals into N combination signals; means for amplifying each of the N combination signals into N amplified combination signals; and means for combining the N amplified combination signals to produce one combined output signal; wherein N is greater than 1.
Also described is a method for reducing distortion using a pre-distortion technique, in an output signal from a power amplifier, comprising the steps of receiving an input signal and dividing it into a main signal and a first signal, attenuating the main signal and outputting an attenuated main signal, processing the attenuated main signal to produce a delayed attenuated main signal, dividing the first signal into a second signal and a third signal, processing the second signal to produce a delayed signal and processing the third signal to produce a distorted signal, combining the delayed second signal and the distorted third signal to produce a distortion signal, dividing the distortion signal N ways into N distortion signals and dividing the delayed, attenuated main signal N ways into N delayed, attenuated main signals, processing each one of N distortion signals through one of N attenuators and one of N phase shifters to produce one of N phase shifted distortion signals, combining each of the N phase shifted distortion signals with one of the N delayed, attenuated main signals in one of N combiners to produce one of N combination signals, amplifying each of the N combination signals to produce N amplified combination signals, and combining each of the N amplified combination signals to produce a combined output signal, wherein N is greater than 1.
Also provided is a feed forward system comprising the described low distortion power amplifier for use as a main amplifier in a feed forward power amplifier.